Hi i have a marshall AVT150 head and cab, just out of curiosity i was wondering what changing the valve in it would do/ if it could improve the sound, or even chance the sound slightly when on overdrive?

If its old and worn down, it will affect the sound negatively but tube rolling itself has very little effect. I dont remember what the tube was for (i think it was different with each valvestate generation) but its job is small.

It will make a difference, I use a JJs ec83 ...I think. Lasts about a year, b ut I kick the crap out of mine. It starts taking longer to start up when I need to change it. But the sound degradation is very slow. You wont hear it until you change it.

On mine everything but acoustic goes thru it, if the tube went out there would be no sound so I disagree with the tube dosn't do much statement.

It will make a difference, I use a JJs ec83 ...I think. Lasts about a year, b ut I kick the crap out of mine. It starts taking longer to start up when I need to change it. But the sound degradation is very slow. You wont hear it until you change it.

On mine everything but acoustic goes thru it, if the tube went out there would be no sound so I disagree with the tube dosn't do much statement.

That's sound logic... So since my Walkman (for the young guys just think iPod with batteries ) won't work without batteries I should be able to hear a difference between brands... Right?

I have AVT50, I changed the valve just once for the original Marshall valve, then replaced it again but couldn't hear any difference in sound.
Maybe it affects the time it takes to heat up, as said before.